At this time, there are a number of commercially available instruments that utilize electrochemiluminescence (ECL) for analytical measurements including drug screening. Species that can be induced to emit ECL (ECL-active species) have been used as ECL labels. Examples of ECL labels include: i) organometallic compounds where the metal is from, for example, the noble metals of group VIII, including Ru-containing and Os-containing organometallic compounds such as the tris-bipyridyl-ruthenium (RuBpy) moiety and ii) luminol and related compounds. Species that participate with the ECL label in the ECL process are referred to herein as ECL coreactants. Commonly used coreactants include tertiary amines (e.g., see U.S. Pat. No. 5,846,485, herein incorporated by reference), oxalate, and persulfate for ECL from RuBpy and hydrogen peroxide for ECL from luminol (see, e.g., U.S. Pat. No. 5,240,863). The light generated by ECL labels can be used as a reporter signal in diagnostic procedures (Bard et al., U.S. Pat. No. 5,238,808). For instance, an ECL label can be covalently coupled to a binding agent such as an antibody, nucleic acid probe, receptor or ligand; the participation of the binding reagent in a binding interaction can be monitored by measuring ECL emitted from the ECL label. Alternatively, the ECL signal from an ECL-active compound may be indicative of the chemical environment (see, e.g., U.S. Pat. No. 5,641,623 which describes ECL assays that monitor the formation or destruction of ECL coreactants). For more background on ECL, ECL labels, ECL assays and instrumentation for conducting ECL assays see U.S. Pat. Nos. 5,093,268; 5,147,806; 5,324,457; 5,591,581; 5,597,910; 5,641,623; 5,643,713; 5,679,519; 5,705,402; 5,846,485; 5,866,434; 5,786,141; 5,731,147; 6,066,448; 6,136,268; 5,776,672; 5,308,754; 5,240,863; 6,207,369 and 5,589,136 and Published PCT Nos. WO99/63347; WO00/03233; WO99/58962; WO99/32662; WO99/14599; WO98/12539; WO97/36931 and WO98/57154.
Commercially available ECL instruments have demonstrated exceptional performance. They have become widely used for reasons including their excellent sensitivity, dynamic range, precision, and tolerance of complex sample matrices. The commercially available instrumentation uses flow cell-based designs with permanent reusable flow cells. Recently, ECL instrumentation has been disclosed that uses reagents immobilized on the electrode used to induce ECL (see, e.g., U.S. Pat. Nos. 6,140,045; 6,066,448; 6,090,545; 6,207,369 and Published PCT Application No. WO98/12539). Multi-well plates having integrated electrodes suitable for such ECL measurements have also been recently disclosed (see, e.g., U.S. application Ser. Nos. 10/185,274 and 10/185,363, entitled “Assay Plates, Reader Systems and Methods for Luminescence Test Measurements”, each filed on Jun. 28, 2002 and hereby incorporated by reference). See also, U.S. application Ser. No. 60/318,293, (Entitled: “Methods and Apparatus for Conducting Multiple Measurements on a Sample” by Glezer et al.), filed on even date herewith, hereby incorporated by reference.
Currently, pH buffers containing inorganic phosphate are employed in many electrochemiluminescence assays. Applicants have discovered that such pH buffers can, in certain assays, interfere with the assay and decrease the performance of the assay.
Accordingly, it would be desirable to find alternative pH assay buffers, compositions containing the same and methods of using the same for use in those assays which are detrimentally effected by pH buffers containing inorganic phosphate. It would also be desirable to find alternative ECL Assay Buffers with improved performance in ECL assays.